The research program is a multidisciplinary collaborative effort in Salvador, Brazil, with a primary focus on the clinical evolution, immunopathology, and epidemiology of Manson's schistosmmiasis and of Chagas' disease. Three Harvard scientists, stationed in Brazil, engaged in collaborative research with counterparts from the Faculty of the Medical School of the Federal University of Brazil (UFBa), and from the Brazilian Ministry of Health through the Fundacao Oswaldo Cruz (FOC) and the Companhas de Saude Publica (SUCAM). The program is sponsored by the Pan American Health Organization (PAHO). Since 1972, three core facilities have been developed: (a) a base laboratory at the medical school in Salvador; (b) clinical resources on the medical wards of the Hospital Professor Edgard Santos; and (c) a censused, studied population in Castro Alves, a rural area 4 hours drive from Salvador, where prevalence rates for schistosomiasis and for Chagas' disease range from 50 to 90%. The program was initiated with a long-term grant from the Wellcome Trust, and by short-term grants from the Clark Foundation and from PAHO, support shortly to expire; the Wellcome Trust support will cease in 1980. Research in progress on Chagas' disease includes: (a) Elucidation of specific morbidity and mortality by repetitive examinations of a defined population at 3 year intervals; (b) Comparison of value of Holter ambulatory electrocardiographic monitoring with standard techniques for characterization of arrhythmias in chronic Chagas' disease; (c) Investigation of the dynamics of transmission in 3 rural areas; (d) Exploration of possible cellular immunologic deficiencies in persistent infections; (e) Study of the role of immunopathologic mechanisms in pathogenesis. Research in progress on schistosomiasis includes: (a) Follow-up of mass chemotherapy with respect to changes in morbidity; alteration in patterns of transmission and in serodiagnostic reactions; (b) Identification of environmental and social factors influencing transmission; (c) Detailed studies on the dynamics of vector snail populations.